In the installation of rigid pipe, particularly cast iron pipe employed for sewage, sanitary and domestic plumbing, it is necessary to couple or clamp together the ends of the pipes in a fluid-tight, aligned relationship. Some such pipes have hubs or flanges on the ends thereof which radiate outwardly from the axis of the pipes and are bolted together, with a gasket therebetween, for a strong, sealed pipe coupling. Although providing a strong coupling, the hubs increase the expense of manufacture. Other such pipes have complementary bell and spigot ends which are sealed by packing oakum in the bell around the spigot, pouring lead over the oakum, and hand-caulking until the joint is pressure-tight. In addition to being a time consuming and expensive procedure, the bell and spigot arrangement has certain limits of application and presents a fire hazard.
To overcome the problems inherent in these prior art couplings, the industry has turned to the use of hubless cast iron pipe. The ends of these pipes are substantially identical and are placed in an abutting relationship for aligned end-to-end sealing. Thus, it is desirable to provide a simple, easily manufactured and applied, economical coupling or clamping assembly for joining hubless pipes in a fluid-sealing end-to-end relationship. The clamping assembly should accommodate slight variations in the external pipe diameters, particularly with hubless cast iron pipes employed for plumbing and sewage applications.
For some time, sand molds have been used in the production of hubless cast iron soil pipe and fittings, to tolerances compatible with the process. Of late, most soil pipes are cast in metal molds where tolerances of a closer nature can be maintained. However, since both processes are in practice, it is necessary to maintain a rather wide tolerance between the maximum and the minimum outside diameter of soil pipe and fittings. Also, since these products must be joined together in a leak-free system, a coupling for them must be compatible with the relatively wide range of dimensions encountered. For instance, for a four-inch nominal size pipe line, one may expect to encounter outside diameter ranging from 4.33 inches to 4.53 inches.
Several couplings for joining soil pipe are in commercial use, both patented and unpatented. The above cross-referenced U.S. Pat. No. 3,233,922 describes that coupling which is probably the most widely used by the industry, in which an annular elastic gasket fits over the adjacent ends of pipe sections to be joined together and is encircled by metal straps or the like which may be contracted to compress the gasket against the pipe ends in a clamping relationship. While this coupling produces a satisfactory joining method under most conditions, it does not provide satisfactory sealing when greater-than-normal internal pressures are encountered, such as in the blockage of the vertical stack of a multi-story building. Further, this prior art clamp or coupling does not provide sufficient inherent structural strength to eliminate the need for additional bracing of the pipeline near the coupling.
Several other clamped-band type soil pipe couplings have been suggested and used previously, and various improvements have been made upon this general type of coupling without obtaining the advantages of the instant invention. For instance, to prevent axial displacement of pipeline sections, an annular groove sometimes is formed near each end of a section, and a coupling housing, which is engagable within the annular grooves, is then fastened around the sections. It is undesirable to provide these grooves in the pipe sections, since it weakens the pipe sections while increasing the expense of manufacture thereof. However, with prior art couplings, omission of this groove has presented difficulty in preventing the ends of the sections from pulling apart, both axially and laterally, when greater-than-normal internal pressures are encountered at the coupling.
Although available couplings have been sufficient in the past, the use of hubless cast iron soil pipes in multi-story construction projects has presented the need for an improvement, so that greater-than-normal internal pressures within the stack or pipeline could be accommodated. For instance, during the construction of multi-story buildings, it is desirous to test these waste stacks for their fluid-tight integrity. These stacks may extend fifty stories or higher, with the internal pressure on a particular coupling increasing with the height of the fluid head above the coupling. Additionally, during construction, or in later use, an obstruction may occur in the lower portion of the stack such that there is a fluid backup within the stack and a subsequent increased internal fluid pressure at the couplings. Accordingly, there is a definite need for an improved coupling for hubless soil pipes in this environment.
It is an object of this invention to join hubless cast iron soil pipe to similar pipe or fittings, with or without spigot beads.
It is a further object of this invention to provide a coupling for hubless cast iron soil pipe which is sufficiently flexible to adapt to varying outside diameters of pipe and fitting ends, yet sufficiently rigid to support and hold the pipe and prevent separation of pipe-to-pipe or pipe-to-fitting joints when subjected to greater-than-normal internal pressures.
Another object of this invention is to improve over prior art compression-only type hubless pipe couplings wherein ends are only held together by the frictional engagement of a flexible seal compressed around the external diameter of the ends of the pipes.
Another object of this invention is to provide a coupling which may be used with a pipe hanger attached to the coupling in order to eliminate the need for separate, additional hanger assemblies near the coupling as well as to eliminate the need for additional bracing of pipes having outside diameters greater than or equal to six inches.
This invention relates to pipe joints, and consists more particularly in new and useful improvements in a joint primarily designed for connecting aligned sections of cast iron pipe having substantially identical ends. In other words, the joint of the present invention is not intended for pipe sections having complementary bells and spigots and is not intended for hubbed pipe sections. Inherent problems in the prior art design of hubless pipe couplings arise from the fact that the sealing pressure and the force needed to hold the pipes end-to-end are applied with a clamping, compressive force around the external diameter of the pipe ends. The instant invention is an improvement over the prior art in that separte means are provided for separate functions, i.e., sealing pressure is applied with tightening bands (as in the prior art) and separate clamp halves are used to hold the pipes end-to-end. It may be noted that while the joint is herein described as used in connection with cast iron pipe, its construction and principle of operation may also be applied to joints for use with other types of pipes, including those formed of rigid plastic material.